In this paper, we propose the combination of Multi Carrier (MC) OFDM/OQAM modulation and CDMA- called MC-CDMA-OQAM system with Space Time (ST) coding in a multiuser context. This combination takes advantages from multicarrier modulation, spread spectrum and spatial time diversity. Indeed, the use of OFDM has proved its ability to fight against frequency selective channels but the insertion of guard interval yields spectral efficiency loss and sensitivity to frequency dispersion due to the use of rectangular pulse shape. Thus, cyclic prefix OFDM is replaced by an advanced filterbank-based multicarrier system OFDM/OQAM that operates without guard interval. However, OFDM/OQAM provides orthogonality only on the real domain, so transmitted symbols must be real valued. In the other hand, the CDMA component has two advantages: multiple access interference cancellation and providing orthogonality in the complex domain. From the orthogonality property provided, the Alamouti ST code can be combined with MC-CDMA-OQAM system.
communication. Using addressing MS1 knows which ME responded. All ME have unique addresses that are determined automatically. Input signals can be allocated to any number of measurement emulators. In this way, measurement of various values on different PC is possible, and because of that, this system is multi-user. For example, one student measures temperature on a PC, another measure pressure only, or fluid movement or any combination.
assuming perfect knowledge of the channel sate information (CSI) and single antenna user terminals (UTs). A downlink hybrid beamforming scheme based on a weighted sum mean square error (WSMSE) optimization problem was proposed for massive MIMO systems . It was shown that the performance degradation is severe when the number of RF chains is smaller than half of the number of antennas. Hybrid approaches explicitly designed for mmW communications were considered in  and . Li et al.  designed an uplink receive beamforming that handles the multiuser interference at both analog and digital stages. However, only single antenna UTs were assumed. A limited feedback hybrid two-stage precoding/combining algorithm was proposed in  for the downlink. In the first stage transmit and receive analog beamforming are jointly computed for each base-station (BS) – user terminal pair assuming interference free links. In the second stage the interference is explicitly mitigated, in the digital domain, by employing a conventional linear zero forcing (ZF) precoding.
In simulations we considered a SC-FDE modulation with blocks of N = 256 useful symbols plus a cyclic prefix of 32 symbols longer than overall delay spread of the channel. The modulation symbols belong to a M-QAM or M-Voronoi constellation (dimensions of M = 16 and M = 64 are considered) and the transmitted data is mapped on constellation’s symbols to optimize energy efficiency. The antennas are equal spaced by d/λ = 1/4 and the amplifiers gains of the antennas follow the sort order of Table 1 for linear and centered arrangements, respectively (under these conditions the directivity in the transmitted constellation is assured by phase rotations of the BPSK components). AWGN channel and a severely time-dispersive channel are considered. The second is characterized by an uniform PDP (Power Delay Profile), with 32 equal-power taps, with uncorrelated rayleigh fading on each tap. For both channels it is assumed a scenario with several users where each user only knows the transmission parameters regarding his data stream. Thus, each user is able to configure the receiver with the correct coefficients g i α 0 i to compensate the
5. After performing step 4, which is a stored crossed site scripting attack combined with a PHP injection attack, continue checking the provided email. When another student browses to the exploited comment page, the PHP script that was injected into the database as a stored cross site scripting attack will be executed upon the rendering of that page. This is because the logic for the comment page prints out whatever value is stored as a comment in the database table. The comment stored in the database at this point is actually PHP code. As the comment page is rendered, that PHP comment from the database is treated like normal code within the page and is thus executed. Since it is PHP code, which is not visible on a web page, the victim user will see no signs of the PHP and will not suspect an attack against him.
Nowadays the Internet provides a wide variety of multi-user communication services over heterogeneous environments, where services are destined for large audiences, independently of the location of users and of the moment when those services are requested. Having this in mind, this paper proposes a QoS Architecture for Multimedia Mobile Multi-user (Q3M) support, to allow mobile operators to control the dissemination of content to large groups of heterogeneous mobile users, independently of the location of the mobile devices. The proposed architecture is structured in three control functions: the Mobile Multi-user control function that provides the required multicast and unicast connectivity, the Service Class control function that dynamically allocates resources of network classes to multicast traffic, and the Session Management control function that manages the dissemination of content to multiple users. Our conceptual analysis reveals that the Q3M architecture provides the key components for the support of multi-user services over heterogeneous mobile environments.
MUSC interacts with SIP to allow users to join or leave a multi-user session. Applications compose a SIP/SDP message to join announced sessions. This message is received by a SIP-proxy in the access-cluster, which can accomplish some authentication, authorization and accounting procedures. After performing its operations, the SIP-proxy forwards the session information to the receiver’s access- Q3MA based on SIP Location Servers. The reception of this information activates the MUSC access-control. After the conclusion of the MUSC operations, the application is informed, by means of a SIP/SDP message, that its request was accepted or not. For multicast-aware devices placed in multicast-aware access-clusters, MUSC also informs the receiver about the multicast channel to be joined by each session-flow (as a consequence, IGMPv3 or MLDv2 messages are sent to the access-router).
Fig. 5 shows the load of RESERVE messages measured in the ingress router of the simulation model. The traced results expose that within all admitted requests, MIRA established 65.9% and MARA 65.7% (less 2) multi-user sessions in the set of experiments. The session blockings in MIRA experiments are of 32.8% for Premium-alike, 32.5% for Gold-alike and 34.6% for Silver-alike, whereas in MARA are of 27.9%, 30.02% and 41.9% respectively. The static per-class MRth maintenance of MIRA lets that all CoSs experience similar session blockings (since the CoSs are also assigned with the same MRth). In contrast, the dynamic re-sizing of CoS’s MRth allows MARA granting congested CoSs with more resources to establish session requests more frequently received (Premium- and Gold-alike in this case). Moreover, this dynamic re- adjustment allows MARA preventing waste of resources and improving bandwidth usage. For instance, consider a scenario where a CoS is more demanded than the others, and that its MRth is not enough to admit all associated requests. Thus, MARA is supposed to provide more resource allocation efficiency than MIRA.
The type of interference experienced in CDMA communication systems is the Multiple Access Interference or the Multi-user Interference. Multiple Access Interference (MAI) is a factor, which limits the capacity and performance of CDMA system. In contrast to FDMA and TDMA techniques which are frequency bandwidth limited, all users transmit in the same frequency band and are distinguished at the receiver by the user specific spreading code. All other signals are not de-spread because they use different codes. These signals appear as interference to the desired user. As the number of users increase, the signal to interference ratio (SIR) decrease until the resulting performance is no longer acceptable. Thus, this multi –user interference must be reduced to achieve higher capacities.
The aim of this paper is to propose and evaluate multi-user iterative block decision feedback equalization (IB-DFE) schemes for the uplink of single-carrier frequency-division multiple access (SC-FDMA)-based systems. It is assumed that a set of single antenna users share the same physical channel to transmit its own information to the base station, which is equipped with an antenna array. Two space-frequency multi-user IB-DFE-based processing are considered: iterative successive interference cancellation and parallel interference cancellation. In the first approach, the equalizer vectors are computed by minimizing the mean square error (MSE) of each individual user, at each subcarrier. In the second one, the equalizer matrices are obtained by minimizing the overall MSE of all users at each subcarrier. For both cases, we propose a simple yet accurate analytical approach for obtaining the performance of the discussed receivers. The proposed schemes allow an efficient user separation, with a performance close to the one given by the matched filter bound for severely time-dispersive channels, with only a few iterations.
To allow scalable traffic differentiation and conditioning of different multi-user sessions (e.g., broadcast video and multimedia streaming), it is assumed that the wired network implements the Differentiated Service (DiffServ) model, and wireless links implement IEEE 802.11e. Such heterogeneity requires mapping flows of sessions into different Class of Service (CoS). This requires a mechanism for on-demand QoS mapping and shielding of devices, sessions and networks from the details of the underlying QoS infrastructure. This can not be done with static mapping approaches. Moreover, the oscillatory network behaviour (e.g., due to re-routing) may require complement QoS mapping with adaptation support to avoid session blocking while keeping accepted sessions with a useful QoS level. This paper introduces Quality of Service Control for Multi- user Sessions (QUALITI) mechanism to control the QoS level of multi-user sessions by integrating QoS mapping, QoS adaptation and network resource allocation. The performance evaluation is done through two sets of tests that analyze QUALITI’s benefits to control QoS level of sessions when experiencing link failure and handover. The
In order to overcome the current MIRA limitations, increase the satisfaction of us- ers and optimize resources in multi-user systems, this paper introduces the Multi-user Aggregated Resource Allocation (MARA) proposal. MARA provides scalable support of IP multi-user sessions, while minimizing signalling, state and processing costs of MIRA per-flow operations. The MARA contribution is performed by dynamically con- trolling the over-provisioning of DiffServ classes and SSM trees. Thus, MARA estab- lishes multiple multi-user sessions without per-flow signalling by combining admission control and surplus network resources (bandwidth and SSM trees) procedures in ad- vance. Multicast aggregation is used to optimize multicast state storage. This paper demonstrates the benefits of MARA in comparison with MIRA to control multi-user sessions regarding session robustness operations under re-routing conditions. The MARA performance evaluation was carried out by simulations, which analyzed band- width/multicast state and signalling overhead under re-routing events.
As consistently mentioned throughout the previous chapter, there is common agreement over the clear advantage to separate the user interface from the functional core in conceptual and implementation architectural models for interactive system. In section III.2.3 we discussed that such conceptual (not necessarily physical) separation leverages on user-interface knowledge in providing design assistance (evaluation, exploration) and run-time services (user interface management, help systems, etc.). This approach should support implementation of internal functionality independent of the user interface fostering reuse, maintainability and multi-user interface development, an increasingly important requirement with the advent of multiple information appliances [Norman, 1998]. The Wisdom interaction model is an external view of the system from the user interface perspective. This model structures the user interface identifying the different elements that compose the dialogue and presentation structure of the system (look and feel), and how they relate to the domain specific information in the functional core. The different elements that compose the Wisdom user-interface architecture are described in detail in section IV.3.2. To specify the interaction model in Wisdom we use the corresponding UML notational extensions described in section IV.4.3. The information in the interaction model corresponds to a technical activity carried out by the user-interface development team. The interaction model is mainly built during the analysis workflow of the elaboration phase. The interaction model influences the presentation and dialogue models devised in the construction workflows.
The interface for the MultiUser Virtual Drawing Board will look in the same manner as shown through the fig. 1. The users working on a design are free to give their respective views on a particular part of the design. The users that agree on the same design will be grouped together and a secondary window is also provided on the main window. This secondary window is provided in order to have the view of the designs made by other users. The number of secondary windows and groups can be controlled. The threshold can be decided by the number of users interested and supporting a particular design. The design instances can be discarded if no users are interested.The proposed idea of the MUVDB will be carried out in three parts. First a message passing model will be designed using sockets and threads. Secondly, an interface will be designed as shown in figure. 1 using swings. Lastly, concurrency or serialization protocol will applied. Through this paper only an idea for building such an application is given and no implementation is been provided for the same. The paper is divided into various sections starting from introduction, problem statement, basic architecture, issues in distributed systems, conclusion and future scope. Through the issues in distributed systems, an attempt is made to compare the proposed idea with the various issues been discussed in this paper. The aim is to state how these various issues can be handled in the multiuser virtual drawing board and the basic advantage behind such an idea.
Most common works for rendezvous in cognitive radio networks deal only with two user scenarios involving two secondary users and variable primary users and aim at reducing the time-to-rendezvous. A common control channel for the establishment of communication is not considered and hence the work comes under the category of ‘Blind Rendezvous’. Our work deal with multi-user scenario and provides a methodology for the users to find each other in the very first time slot spent for rendezvous or otherwise called the first- attempt-rendezvous. The secondary users make use of the history of past communications to enable them to predict the frequency channel that the user expects the rendezvous user to be. Our approach prevents greedy decision making between the users involved by the use of a cut-off time period for attempting rendezvous. Simulation results show that the time-to-rendezvous (TTR) is greatly reduced upon comparison with other popular rendezvous algorithms. Keywords:
This paper looks into the relationship of user characteristics, user involvement and technology acceptance, also try to find the relationship of the above three variables and library automation system usage. By interview and questionnaire study, the results are described, according to the analysis of the relative literature and the main conclusions, the researcher offers some suggestions for improving the system usage.
Stands for real time de-provisioning. Just-intime provisioning indicates the federation of user accounts without sharing prior data, based on some trust model. Service Provisioning Markup Language (SPML) provides XML based structures for representing provisioning or de-provisioning requests intended for identity lifecycle management . SPML can make use of Service Administered Markup Language (SAML) assertions and facilitate a complete trust model between senders and receivers. SAML defines an XML based framework for exchanging security information for enabling SSO or identity federation regardless of the underlying architecture. OASIS Security Services is currently working on developing a SAML 2.0 profile for SPML. SAML can help SPML to establish trust and quantity, a subject against which the SPML provisioning request is targeted. This makes just-in- time provisioning and real time de-provisioning possible.
It can be stated that most small communities have the capacity to influence more people be- cause they possess greater knowledge of issues, products or services, which in turn leads to an increased confidence by the people who visit the community. As can be seen in figure 2.2(b), retail sites and brand sites are those that influence more people because the degree of knowl- edge they have about the product/service is greater, which facilitate decision-making process in overall purchases. With regard to the creation of influence by brands and influencers, blog- ging is the primary publishing tool, and about a third of influencers say they have been blogging for five or more years. Most bloggers (about 52%) operate 2 to 5 blogs, while 43% operate just one. Only 5% of bloggers operate 6 or more blogs. The primary method for bloggers is text, but photos and microblogging (e.g., Twitter) come in at 38% and 31%, respectively. Video and audio are the least used methods. Bloggers also say that other bloggers are very influential when it comes to choosing their own content to publish. When it comes to measuring their own success, blog/website page view rank highest but social following (e.g., Facebook Likes, Twitter followers) and user interactions (e.g., comments) also rate high.